Changes in input/output (I/O) timing parameters can severely impact I/O performance, particularly with respect to high performance or high frequency I/O design. Typically, an I/O circuit (e.g., a buffer) is designed for operation within strict timing guidelines. Failure to operate with the intended timing parameters may prevent the buffer from operating properly. Alternatively, failure to operate within these timing parameters may prevent the buffer from interfacing properly with other circuitry that does adhere to the timing parameters.
Variations in temperature may cause the buffer circuitry to operate outside of the intended timing parameters. Process variations introduced during manufacture of the buffer circuitry can cause variations that detract from optimal performance even if the buffer circuitry is still operating within intended timing parameters.
The buffer circuitry is typically designed to operate at specific voltages or within specified voltage ranges. In practice, however, the voltages are typically within some tolerance factor of the specified voltage or range. Changes in voltage, however, tend to cause a shift in the actual timing parameters of the buffer circuitry.
Alternatively, the collective effect of process, voltage, and temperature (PVT) variations may prevent the buffer from functioning or prevent the buffer from performing in accordance with the intended timing parameters. Lack of adequate compensation for individual I/O components can result in departure from optimal performance if, for example, the timing parameters change.
Some I/O circuitry must translate one type of logic to another type of logic. For example, an integrated circuit may have Gunning Transceiver Logic (GTL) based I/O buffers with a complementary metal oxide semiconductor (CMOS) logic based core. The I/O circuitry must be able to translate between GTL and CMOS levels in order to properly function. PVT variations within the GTL circuitry or the CMOS circuitry separately or collectively can produce timing parameter changes that prevent the I/O circuitry from operating at optimal performance levels.